Electronic techniques have been applied to the weighing art. Electronic scales and weighing systems have been developed which provide a relatively rapid readout in digital format without the use of springs and similar mechanical devices. A particularly useful system involves the use of a load cell or similar transducer which provides an analog voltage or signal which is proportional to the weight of an unknown load to a high degree of linearity. Amplifiction and analog-to-digital conversion is employed to provide a digital output signal corresponding to the weight of the load. Systems of this type have been developed commercially which are capable of displaying the weight of a load accurately to the nearest hundredth of a pound within several seconds.
Weight-price labeling systems have also been developed using the above format in conjunction with commercially available solid state microprocessors in which the net weight of an article is computed by subtracting a set tare weight from the measured gross weight of an article and then computing the article price by multiplying the net weight by the price per unit weight. In these systems, a keyboard is employed to enter the price per unit weight into the microprocessor and also to enter the tare weight data. Optionally, the tare weight data may be entered directly from the scale by loading a representative empty article container on the scale, the system being provided internally with circuitry which allows entry of this measurement as the set tare weight data when this option is exercised.
In conjunction with visual display of the set tare weight, net weight, price per unit weight and computed article cost, a label printing device is operated which prints the desired information on a label for application to the article package.
Systems of this latter type have found wide applicability in retail outlets such as supermarkets and the like, and are likely to encounter increasing demand for various reasons.
However, such systems require sophisticated and expensive electronic circuitry in order to attain and maintain the accuracy which is inherent with present electronic weighing transducers. For example, although a state of the art load cell or similar transducer will be highly linear over a particular load range and therefore is capable of yielding weight readings of high accuracy within that range, normal electronic drift in the equipment which processes the transducer signal may well introduce error which substantially reduces the overall accuracy. Thus, substantial effort has been expended in order to establish a stable "zero" reference from which the weight measurements are taken. Obviously, if stable "zero" is not achieved, the measured gross weight which provides the basis for all computations will correspondingly be in error.
A further problem with present systems is the fact that due to the discrete-step nature of any analog-to-digital conversion, the least significant bit obtained by the conversion is an approximation whose accuracy is only .+-.1/2 the least significant bit.